Compact vehicle based rear and side obstacle detection system including multiple antennae

ABSTRACT

A rear and side object detection system for a vehicle based on monolithic millimeter wave integrated circuit technology. A multiple antenna configuration is employed that defines six sensing regions to the right, left and the rear of the vehicle. A sixth sensing region is defined at the right side of the vehicle, a second sensing region is defined at the right side and rear of the vehicle and overlaps the sixth sensing region, a fourth sensing region and a first sensing region extend from the rear on both sides of the vehicle in the adjacent lanes, a third sensing region is defined at the left side of the vehicle and a fifth sensing region is defined at the left side and rear of the vehicle and overlaps the second and third sensing regions. A right side warning signal is issued if an object is detected in a right side detection zone defined by the sixth sensing region or a portion of the second sensing region that does not overlap the fourth or fifth sensing regions. Likewise, a left side warning signal is issued if an object is detected in a left side detection zone defined by the third region and a portion of the fifth sensing region that does not overlap the second or first sensing regions. A back-up warning signal is issued if an object is detected in an overlap region between the second and fifth sensing regions.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to a rear and side object detectionsystem for a vehicle and, more particularly, to a rear and side objectdetection system for a vehicle that incorporates an antennaconfiguration that defines overlapping antenna fields around the vehiclewhere the antenna fields combine to give an accurate detection ofobstacles within a desirable obstacle detection region.

2. Discussion of the Related Art

For current vehicle transportation, there is a significant number ofincidences involving vehicle collisions with obstacles, such as othervehicles, when the vehicle is changing travel lanes or merging, and whenthe vehicle is operating in reverse. The main reason why the lanechange/merge and reverse operation incidences occur is because thevehicle operator is unaware of the obstacles in the vehicle's intendedpath. Many factors relate to why the vehicle operator would be unawareof the obstacles. These factors include operator fatigue, carelessness,distraction by other conditions, and blocked vision. This suggests thatmany of these crash incidences can be avoided by vehicle basedcountermeasures that inform the vehicle operator of the presence of anobstacle when the vehicle operator initiates a lane change or back-upmaneuver.

Currently, progress is being made in the applicable technological fieldsto achieve an effective rear and side object detection system thatinforms a vehicle operator of an impending collision with many types ofobjects that may be present within the vehicle's intended path. In mostpractical detection systems of this type, radar technology is utilized.Particularly, a radio wave signal at a desirable frequency is emittedfrom the detection system to define a desirable sensing zone around thevehicle, and reflected signature signals from objects within the zoneare received by the system to be analyzed. Positional information fromthe signature signals and the relative timing between the transmittedradio wave signal and the reflected signature signals provide anindication of the location, distance and speed of the objects. Abackground discussion of typical obstacle detection systems known in theart can be found in U.S. Pat. Nos. 5,087,918; 5,008,678; 4,349,823 and3,697,985.

It does not appear that the current technology has reached a level thatwould make radar detection systems feasible in a wide variety of massproduced vehicles. This is because of a number of necessary designcriteria required for a practical detection system. Generally, thedetection system must be low cost and readily adaptable to various typesof vehicles with respect to consumer demands and industry standards.More importantly, the detection system must be reliable in that thesystem must give a warning indication of an obstacle of the type thatmay cause a collision for a high percentage of the times, and notprovide a warning or nuisance signal for those objects that do notprovide a chance of collision.

To achieve reliable object detection, the detection system mustaccurately define sensing zones around the vehicle. The requirement forhighly defined sensing zones can be realized by understanding thefollowing situation. The detection system must emit a signal of asufficient power that will cause a small child to generate a significantreflection signature signal if the child is behind the vehicle in apotentially hazardous position. However, it would be undesirable toprovide a warning signal of a metal obstacle that was significantlydistanced from the back of the vehicle where it would not be a potentialcollision hazard. Because the metal object would provide a much greaterreflection signature than the child when at the same distance for thesame power level, the design of the system must define the sensing zonesto separate these two events to be practical.

To detect objects in the proximity of a vehicle to be effective againstlane change/merge and back-up collisions, the detector system must beable to cover specific areas to the left, right and back of the vehicle.In order to create this necessary coverage without sacrificingaesthetics and to avoid packaging problems, a multiple detector systemconfiguration is necessary. However, it becomes important from a designstandpoint to limit the number of power sources and antenna in thesystem because of space and cost constraints.

What is needed is a rear and side obstacle detection system thataccurately defines effective sensing areas around a vehicle so as togive a high probability of detection when a potential collision causingobstacle is within the sensing areas, and prevent the system fromindicating an obstacle is present when one is not present in the sensingareas. It is therefore an object of the present invention to providesuch a rear and side object detection system.

SUMMARY OF THE INVENTION

In accordance with the teaching of the present invention, a rear andside obstacle detection system that provides a warning of an obstaclethat is within specified sensing regions around a vehicle is disclosed.A multiple antenna configuration is employed that defines six sensingregions to the right, left and rear of the vehicle. The antennaconfiguration is designed such that the sensing regions accurately sensestrategic areas around the vehicle that are limited to adjacent lanes oneither side of the vehicle and an appropriate back-up area behind thevehicle. A sixth sensing region is defined at the right side of thevehicle, a second sensing region is defined at the right side and rearof the vehicle and overlaps the first sensing region, a fourth sensingregion and a first sensing region extend from the rear on both sides ofthe vehicle along the adjacent lanes, a third sensing region is definedat the left side of the vehicle, and a fifth sensing region is definedat the left side and rear of the vehicle and overlaps the second andthird sensing regions.

A right side warning signal is given if an obstacle is detected in aright side detection zone defined by the sixth sensing region or aportion of the second sensing region that doesn't overlap the fourth orfifth sensing regions. Likewise, a left side warning signal is given ifan obstacle is detected in a left side detection zone defined by thethird sensing region and a portion of the fifth sensing region that doesnot overlap the second or first sensing regions. A back-up warningsignal is given if an obstacle is detected in an overlap region betweenthe second and fifth sensing regions. The fourth and first sensingregions detect obstacles that are traveling at a speed that will causethe obstacle to enter the right or left side detection zones within apredetermined period of time so as to issue an appropriate right or leftside warning signal.

In one embodiment, the detection system comprises two sensing unitspositioned at the rear of the vehicle on the left and right sides. Eachof the sensing units incorporates three antenna arrays speciallydesigned to define the six sensing regions. The sensors are based onmonolithic millimeter wave integrated circuit technology such that asingle power source associated with each unit provides power to thethree antenna arrays.

Additional objects, advantages, and features of the present inventionwill become apparent from the following description and appended claims,taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a rear view of a vehicle incorporating a rear and sideobstacle detection system according to an embodiment of the presentinvention;

FIG. 2 is a blown apart perspective view of one sensor associated withthe rear and side obstacle detection system of FIG. 1;

FIG. 3 shows a block diagram of the rear and side obstacle detectionsystem of the present invention;

FIG. 4 shows a block diagram of the operation of the rear and sideobstacle detection system of the invention;

FIG. 5 shows a block diagram of a spectrum estimation device of theinvention.

FIG. 6 is a top view of the vehicle of FIG. 1 depicting a plurality ofsensing regions established by the rear and side obstacle detectionsystem around the vehicle according to an embodiment of the presentinvention; and

FIG. 7 is a perspective view of the vehicle of FIG. 6 depicting theplurality of sensing regions.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description of the preferred embodiments directed to arear and side obstacle detection system for detecting obstacles around avehicle is merely exemplary in nature and is in no way intended to limitthe invention or its applications or uses.

FIG. 1 shows a rear view of a vehicle 10. The vehicle 10 is intended torepresent any type of vehicle adaptable to operate on a conventionalhighway system. The vehicle 10 includes a left side sensor 12 positionedwithin a left end of a bumper 14 associated with the vehicle 10 and aright side sensor 16 positioned within a right end of the bumper 14. Aswill be discussed in detail below, the sensors 12 and 16 emit a radiowave signal that defines sensing regions (see FIGS. 6 and 7) around aleft side 18, a right side 20 and a rear area 22 of the vehicle 10. Thesensors 12 and 16 are shown positioned at opposite ends of the bumper 14as one possible strategic location to define the desirable sensing area.However, as will be appreciated by those skilled in the art from thediscussion of Applicant's embodiments and the prior art, the sensors 12and 16 can be positioned at other locations on the vehicle 10 withoutsignificantly effecting the sensing regions around the vehicle 10. Forexample, the left side sensor 12 can be positioned at some location onthe left side 18 of the vehicle 10, and the right side sensor 16 can bepositioned at some location on the right side 20, as well as beingpositioned at other locations on the rear area 22 of the vehicle 10,without departing from the scope of the invention. U.S. patentapplication Ser. No. 08/177,266 to Chen et al., assigned to the assigneeof the instant application, and herein incorporated by reference,discloses sensors of the types of sensors 12 and 16 being positionedwithin side view mirrors 24 of the vehicle 10.

FIG. 2 shows a blown apart perspective view of the components of thesensor 12 according to an embodiment of the present invention. It willbe understood that the sensor 16 includes the identical components ofthe sensor 12. FIG. 3 shows a block diagram of a rear and side detectionsystem 28 according to one embodiment of the present inventionincorporating the sensors 12 and 16. The sensor 12 includes a basemember 30 on which is secured various sensor components. A connectorlead frame 32 is provided to connect the sensor 12 to other circuitcomponents, such as a system controller 34 and a vehicle battery (notshown). An intermediate frequency (IF) printed circuit board 40 ispositioned on the base member 30 to provide connections from the leadframe 32 to an integrated circuit chip board 42. The chip board 42includes a monolithic millimeter wave integrated circuit (MMIC) 44, apatch antenna array 46, a first end-fire slot antenna array 48 and asecond end-fire slot array antenna 50. A cover 54 covers the sensor 12and acts as a suitable protective layer to the sensor 12 from theenvironmental conditions that would exist at the rear of the vehicle 10.Additionally, the cover 54 is aesthetically matched to the design of thevehicle 10. U.S. patent application Ser. No. 08/177,266 referenced abovedepicts an alternate configuration of the different layers andcomponents of a sensor of the type of the sensor 12 that is within thescope of the present invention.

The reason for the particular configuration of the antenna arrays 46, 48and 50 will become apparent from the discussion below. It is stressed,however, that these antenna arrays are used by way of a non-limitingexample in that other types of antennas, including dipoles and feedhorns, can be incorporated within the scope of the invention. U.S.patent application Ser. No. 08/177,266 referenced above discusses othertypes of antenna configurations that may be suitable for the purposesdescribed herein.

The sensor 12 utilizes MMIC technology to provide a suitable transceiver58 for the purposes described herein. U.S. Pat. No. 5,315,303 issued toTsou et al, assigned to the assignee of the instant application andherein incorporated by reference, discloses a monolithic millimeter waveintegrated circuit transceiver and associated circuitry that isapplicable for the purposes of the present invention. A generaldescription of the operation of the sensors 12 and 16 will be givenbelow that is adequate to describe the embodiments of the invention.However, it will be understood that a more detailed discussion of theoperation of the sensor 12 can be gleaned from a detailed analysis ofU.S. Pat. No. 5,315,303.

An appropriate voltage signal is applied from the vehicle batterythrough the controller 34 to voltage regulators 60 within the sensor 12.A temperature control device 62 monitors the temperature of the sensor12. The sensor 12 is activated when an input signal from the controller34 is applied to a digital signal processor (DSP) 64. The DSP 64 appliesan output signal to a sweep generator 66 to generate an appropriatevoltage signal. The voltage signal is applied to a voltage controlledoscillator (VCO) 68. The VCO 68 generates a millimeter wave frequencysignal at the desirable frequency that is applied to a series ofamplifiers 70. The amplified millimeter wave frequency signal is thensystematically applied to a series of antenna 72 through a rotatingswitch 74 to radiate the frequency signal into space. The antenna 72 areintended to represent the patch antenna array 46 and the end-fire slotantenna arrays 48 and 50.

Signals that are reflected off of objects within the antenna fieldsdefined by the antenna 72 are received by the antenna 72 and applied toa mixer 76 through the switch 74. The mixer 76 mixes the reflectedsignal with the frequency signal from the VCO 68 for timing purposes.The mixed signal from the mixer 76 is applied to an analog-to-digitalconverter 78 through a series of amplifiers 80. The digital signalrepresentation of the reflected signal is applied to the DSP 64 forsignal processing in a manner that will be discussed in greater detailbelow. If the DSP 64 determines that a warning signal should be issuedas a result of the reflected signal, the DSP 64 will output anappropriate signal to the controller 34 that will in turn activate asuitable warning device (not shown).

The sensors 12 and 16 provide object detection and range/velocitymeasurement functions of detected objects, and the controller 34performs the final warning decision processing as well as overall systemcontrol, self-test and vehicle interfacing. Further, the controller 34provides watch dog functions and overall system diagnostics. A series ofinput and output lines 82 are connected to the controller 34. Inputlines are provided to provide input signals to the controller 34 of whenthe sensors 12 and 16 should be activated. In one example, adetermination of whether an obstacle exists at the right side of thevehicle 10 will be made when a right turn signal (not shown) is switchedon, a determination of whether an obstacle exists on the left side ofthe vehicle will be made when a left turn signal (not shown) is switchedon, and a determination of whether an obstacle exists at the rear of thevehicle 10 will occur when the vehicle 10 is switched into reverse. Inan alternate example, the sensors 12 and 16 can be continuouslyactivated to provide an indication as to whether an obstacle is aroundthe rear and side of the vehicle 10 at all times of vehicle use.Indications of whether obstacles are present when the sensors 12 and 16are activated is applied through the controller 34 to various types ofwarning devices (not shown), such as audible alarms and visual signals.For different applications, different levels of warnings can be given.For example, the system 28 can be designed such that a visual warningsignal is given whenever an obstacle is within the range of the antenna72, and a visual signal and an audible alarm can be given when anobstacle is in a zone that is critical for a particular left, right orback-up maneuver in response to activation of the left and right turnsignals and the reverse gear.

The system 28 uses millimeter wave radar signals with a FM-CW chirpedwave form. The FM-CW approach is well suited to low peak power MMICtransmitters, and is compatible with the current generation of low costdigital signal processors. Millimeter wave frequencies are desired toutilize small antenna, and to accommodate a 500 MHz bandwidth to enableone foot range resolution. One foot range resolution is desirable tofine tune the antenna coverage using range cutting to faithfully followthe desired detection areas. The patch antenna array 46 and the slotantenna arrays 48 and 50 transmit an appropriate millimeter wave radarsignal, and receive reflected signals.

In one embodiment, the radar signals are emitted at 20 mW having greaterthan a 23 dB signal-to-noise ratio. This yields signal pulse detectionprobabilities of approximately 98% and negligible false alarms fortargets with fluctuating cross sections. Five chirped pulses aretransmitted within a 5 msec update period and a proximity detectioncriteria of three out of five return pulses exceeding adaptivethresholds (discussed below) in order to declare a detection. To providethe necessary processing capabilities, the controller 34 includes asuitable microprocessor such as the Motorola MC68HCO5B6 8-bitmicrocontroller having 6k bytes of masked read only memory (ROM), 512bytes of erasable programmable read only memory (EPROM) and 256 bytes ofrandom access memory (RAM). The DSP 64 can be a Texas InstrumentsTMC320C10 16-bit processor including 3k bytes of masked ROM and 288bytes of RAM. The millimeter wave radar signal can be transmitted atvarious millimeter wave frequencies in the GHz frequency bands. Forexample, suitable frequency bands include 37.5-38.5 GHz, 76-77 GHz,92-95 GHz, 140 GHz and 153 GHz. These components and parameters are justexamples of suitable devices and system operations as it will beappreciated by those skilled in the art that others will be equallyapplicable within the scope of the invention.

FIG. 4 shows a block diagram of a system 100 depicting the operation ofa portion of the DSP 64 when it receives a reflected signature signal.The discussion below will be general in nature as adequate for thepresent invention. A more detailed description of this operation can befound in U.S. patent application Ser. No. 08/173,540, filed Dec. 23,1993, assigned to the assignee of the instant application, and hereinincorporated by reference. The system 100 includes a data samplingdevice 102 that samples an output of the mixer 76 through theanalog-to-digital processor 78. The mixer 76 combines the transmittedsignal with the reflected signal to generate a mixer output signalrelated to the range of a detected object. If multiple objects aredetected, the mixer output signal will be a sum of frequenciescorresponding to each object. An output of the data sampling device 102is applied to an energy estimation device 104 that estimates a totalenergy of the sampled mixer output signal. An automatic gain controldevice 106 generates a gain control signal for an automatic gainamplifier (not shown) associated with the sensor 12.

A spectrum estimation device 108 receives the sample data signal fromthe sample data device 102 to estimate the spectrum of the sampled mixeroutput signal. A more detailed block diagram of the spectrum estimationdevice 108 is shown in FIG. 5. A time domain window device 110multiplies the sampled mixer output signal generated by the sample datadevice 102 with a time domain window function, for example a raisedcosine function, to generate a windowed signal. The time domain windowdevice 110 decreases spectrum leakage and outputs the windowed signal toa fast fourier transform (FFT) device 112 which generates a frequencyspectrum signal. The frequency spectrum signal includes a series ofspectral components.

The frequency spectrum signal is applied to a magnitude determiningdevice 114 that calculates the magnitude of the spectral components, andgenerates a magnitude range profile signal. The magnitude range profilesignal includes a plurality of range bins where each range bin isassociated with a spectral component and contains the magnitude of theassociated spectral component. The magnitude of each spectra-componentis related to signal strength at a particular frequency. Signal strengthrelates to the presence or absence of objects at a given range. Inaddition, the frequency of a peak of the frequency signal is related tothe distance of a target.

The magnitude range profile signal is then applied to a noiseequalization device 116. Because the sampled mixer signal has a noisecharacteristic which increases with decreasing frequency, the magnituderange profile signal is equalized by the noise equalization device 116to produce an equalized range profile signal having a noise floor thatis constant with respect to frequency. The equalized range profilesignal is applied to an averaging or integration device 118 whichintegrates the equalized range profile signal with prior equalized rangeprofile signals to increase the signal-to-noise ratio so as to increasethe detection probability.

The averaging device 118 generates an integrated range profile signalwhich is applied to an adaptive threshold device 120. The adaptivethreshold device 120 defines a moving window that includes a pluralityof range bins. The adaptive threshold device 120 evaluates the signalstrength of each range bin and generates target flags in the range binsto indicate the presence or absence of an object. The adaptive thresholddevice 120 is implemented with one form of a constant false alarm ratealgorithm to have a predictable false alarm rate based on thesignal-to-noise ratio of the system 100. This algorithm determines theamplitude threshold which potential objects must be above to berecognized. Anything below the threshold is discarded as noise. Thethreshold changes in both range and time, and thus is adaptive tochanging conditions of clutter, object size and distance. Various typesof adaptive threshold techniques are discussed with reference to U.S.patent application Ser. No. 08/173,540 referenced above.

For the lane change target prediction mode of operation, a 2D parameterestimation device 122 determines target distance and velocity. The 2Dparameter estimation device 122 performs computations on a 2D objectspace array generated by the adaptive threshold device 120, andgenerates a 2D estimation signal including components related to thespeed of and distance to possible detected objects. Only objects greaterthan the threshold range profile signal are analyzed and only the objectpaths which correlate closely enough to constant velocity motion passthe thresholding. An object is valid if it persists over enoughthresholding intervals, and if its path is correlated to a relativelynon-accelerating path. This estimate is then used to determine if theobject will be within side detection zones within one second as will bediscussed below. The algorithm utilizes the transform from twodimensional range-time space to range-time velocity space. Thisalgorithm has superior clutter rejection properties and rejects objectsthat are out of the allowed velocity limits.

For rear and side object detection where only range is needed, the 2Dparameter estimation algorithm is not performed, and the process movesto a target detection decision device 124. A target decision algorithmdetermines whether the object is valid and if it should be sent on tothe controller 34. If the target decision device 124 determines that anobject is present that may cause a potential collision, the targetdecision device 124 outputs a signal to an output target range and speeddevice 126 to give the appropriate object range and speed data to thecontroller 34.

FIG. 6 shows a top view and FIG. 7 shows a perspective view of thevehicle 10 and a plurality of sensing regions defined by the sensors 12and 16 at the left side 18, the right side 20 and the rear area 22 ofthe vehicle 10. Each antenna array of the sensors 12 and 16 radiates afrequency signal into space that is limited to a particular shape anddistance so as to define a sensing region such that a reflected signalfrom an object in the sensing region is detected by the antenna arraythat created the region. Particularly, the patch antenna array 46 of thesensor 12 is configured to define a sensing region 130, the end-fireslot antenna array 48 is configured to define a sensing region 132, andthe end-fire slot antenna array 50 is configured to define a sensingregion 134. Likewise, the patch antenna array of the sensor 16 isconfigured to define a sensing region 136 and the end-fire slot antennaarrays of the sensor 16 are configured to define sensing regions 138 and140. As would be well understood to those skilled in the art, the typesof antenna arrays discussed herein can be accurately designed atparticular power levels to be limited to desirable antenna fields. Theshape of the sensing regions 132, 134, 138 and 140 generated by theend-fire slot antenna arrays are typical 90° beam width antenna fieldsproduced by a dipole antenna.

In one example, the end-fire slot antenna arrays are configured to givea 15° beam width in the vertical direction to limit the verticalcoverage of the sensing regions 132, 134, 138 and 140 to the height ofthe vehicle 10, and a 90° beam width in the horizontal direction. Thesensing regions 132, 134, 138 and 140 extend out from the vehicle 10 toa distance within the range of about nine feet to about twelve feet tolimit the coverage area to the adjacent lanes. The power of the sensors12 and 16 can be adjusted to increase or decrease this area for specificapplications. The patch antenna arrays have a 15° beam width with a 13°bore sight angle to provide for long range coverage without spill overinto either the lane occupied by the vehicle 10 or two lanes over oneither side of the vehicle 10. In this example, the regions 130 and 136extend to about fifty feet behind the vehicle 10. It is stressed thatthe specific beam coverage of the different sensing regions 130-140 canbe adjusted by altering the power and antenna configuration and size toprovide for different modifications of coverage for differentapplications within the scope of the invention.

Appropriate algorithms associated with the digital signal processors ofthe sensors 12 and 16 allow the system 28 to use logic to analyzedetection in the six sensing regions 130-140 to provide a reliableindication of potential collision threatening obstacles. Range andvehicle speed of detected obstacles are combined in the digital signalprocessors to determine whether a warning is to be issued.

Sensing coverage for lane changing and merging purposes is attained onthe right side 20 of the vehicle 10 by defining a right side detectionzone by logically combining the sensing regions 132, 136, 138 and 140.The right side detection zone is defined by the sensing region 140 and aportion 142 of the sensing region 132. A front portion of the right side20 is covered by the sensing region 140. A detection within the sensingregion 140 will produce a right side detection warning. For detection ofa rear portion of the right side 20 of the vehicle 10, the decision toissue a warning is based upon the presence or absence of objectdetections at the same positional location relative to the vehicle asdetermined by range measurements of a detected object within the sensingregions 132, 136 and 138. If an object is detected in the sensing region132 at a particular position, but an object is not detected at thatposition in either the sensing region 136 or the sensing region 138,then the detected object is contained in the portion 142 of the region132 that does not include any of the regions 134 and 138. In thissituation a right side warning is issued. If, however, an object isdetected at a particular position in the sensing region 132, and is alsodetected at that position in one of the detecting regions 136 or 138,then the object is not within the region 142, and therefore the objectis not within the right side detection zone. Thus, the right sidewarning signal is not activated.

The same logic holds true for a left side detection zone at the leftside 18 of the vehicle 10 determined by a logical combination of thesensing regions 130, 132, 134 and 138. The left side detection zone isdefined by the sensing region 134 and a portion 144 of the sensingregion 138. A front portion of the left side 18 is covered by thesensing region 134. A detection within the sensing region 134 willproduce a left side detection warning. For detection of a rear portionof the left side 18 of the vehicle 10, the decision to issue a warningis based upon the presence or absence of object detections at the sameposition in the sensing regions 130, 132 and 138. If an object isdetected in the sensing region 138 at a particular position, but anobject is not detected at that position in either the sensing region 130or the sensing region 132, then the detected object is contained in theportion 144 of the region 138 that does not include the regions 130 and132. In this situation, a left side warning signal is activated. If,however, an object is detected in the sensing region 138 at a particularposition, and is also detected in either of the sensing regions 130 or132 at that position, then the object is not within the portion 144, andtherefore the object is not within the left side detection zone. Thus,the left side warning is not activated.

In order to detect approaching vehicles moving relative to the vehicle10 in the adjacent lanes to the vehicle 10 that may enter the left orright side detection zone for lane changing and merging purposes, thelong range sensing regions 130 and 136 are employed. For a detectedobject in the sensing regions 130 and 136, the change in range of theobject will be determined, and a left or right side warning signal willbe issued if the predicted time for that object to enter the left orright side detection zones is less than a predetermined time interval. Aone second time interval is used by way of a non-limiting example. Othertime periods may also be applicable for different environments. The onesecond time interval is selected as the time an approaching vehicle willhave time to stop before colliding with the vehicle 10 for relativevehicle speeds of about 30 mph. This long range coverage has beendesigned to detect target objects only in the adjacent lane out to adistance of about 50 feet.

In order to cover a detection zone behind the vehicle 10, a combinationof the sensing regions 130, 132, 136 and 138 are employed. The system 28will issue a back-up warning if an object is detected in an overlapregion 146 of the sensing regions 132 and 138. In other words, theantenna arrays that create the sensing regions 132 and 138 must eachdetect an object at the same position for a back-up warning to beissued. In order to avoid an ambiguity that may exist when coincidentobjects are present separately in the sensing regions 132 and 138 at thesame range and outside of the overlapping region 146, object detectionsin the sensing regions 130 and 136 are also monitored for back-updetection. If an object appears in the sensing region 130 at the sameposition as an object in the sensing region 138, or if an object appearsin the sensing region 136 at the same position as an object in thesensing region 132, then it is assumed that two separate objects arepresent off to the side of the region 146, and therefore no back-upwarning is issued.

The system 28 also has the capability of providing back-up warnings forimpending backing collisions which may occur during curved path back-upmaneuvers. Simple analysis can show that for many curved path back-upmaneuvers, the region 146 may not be applicable to provide a timelywarning. This is because the object will not necessarily be in theregion 146 until just before impact. Therefore, it may be necessary tomonitor all of the sensing regions 130-140 during reverse operation.Right side 20 coverage could be produced by utilizing the area of region132, but excluding the areas of regions 138 and 140. Likewise, left side18 coverage could be produced by utilizing the area in region 138, butexcluding the areas in regions 132 and 134.

The foregoing discussion discloses and describes merely exemplaryembodiments of the present invention. One skilled in the art willreadily recognized from such discussion, and from the accompanyingdrawings and claims, that various changes, modifications and variationscan be made therein without departing from the spirit and scope of theinvention as defined in the following claims.

What is claimed is:
 1. A rear obstacle detection system for detectingobstacles around a vehicle, said system comprising:at least oneradiation beam signal source that generates a frequency signal; aplurality of antenna responsive to the frequency signal, each of theplurality of antenna transmitting a radiation beam in a controlledmanner to define a plurality of separate sensing regions around thevehicle, wherein a first sensing region is defined around a right siderear portion of the vehicle and a second sensing region is definedaround a left side rear portion of the vehicle, said first and secondsensing regions overlapping to define a rear detection zone directlybehind the vehicle, said plurality of antenna further defining a thirdsensing region that extends behind and to a right side of the vehicleand overlaps the first sensing region and a fourth sensing region thatextends behind and to a left side of the vehicle and overlaps the secondsensing region, said plurality of antenna being responsive to radiationsignals that are reflected off of obstacles within the first, second,third and fourth sensing regions so as to generate a signal indicativeof a reflected intensity of the reflected signal; and a control deviceresponsive to the signals from the plurality of antenna, said controldevice generating a rear obstacle detection signal if an object isdetected in the first and second sensing regions at approximately thesame position within the rear detection zone, and said control devicepreventing the rear obstacle detection signal from being generated if anobject is detected in the third and fourth sensing regions outside ofthe rear detection zone.
 2. The system according to claim 1 wherein therear detection zone extends behind the vehicle within a range ofapproximately nine feet to approximately fifteen feet.